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Pittsburgh Mosquito Forecast

Today's mosquito activity in Pittsburgh, the week ahead, and what to do about it. Updated hourly.

Bite Index · Sunday, November 8

Low

Mosquito activity in Pittsburgh is low today.

Few mosquitoes. You may see one or two at dusk near water.

About normal for November in Allegheny County (typically around 0).

  • Off-season: even with rain and warmth, populations are a fraction of summer's.
  • Tonight: a cool 48°F evening, light wind — poor flying weather, so fewer bites than the population alone would suggest.
  • At a two-week average of 57°F, larvae develop slowly and the population stays small whatever the rain.

The week ahead

Each day's Bite Index, from this week's weather and the rain that is still hatching. Forecast days get less certain as the week goes on.

  1. Today
    2Low59°/41°dry
  2. Mon
    2Low53°/39°dry
  3. Tue
    2Low61°/37°dry
  4. Wed
    2Low61°/46°dry
  5. Thu
    0Low55°/48°0.5 in
  6. Fri
    0Low49°/38°0.1 in
  7. Sat
    0Low39°/38°0.1 in

Protect tonight

You can probably skip repellent tonight.

  1. If you're near a creek, pond or heavy shade at dusk, a light application on ankles and arms is plenty.
  2. Good night to tip out any containers holding water; what you empty now won't hatch next week.
Which repellent, and how much: DEET vs picaridinBest natural repellents

Why Pittsburgh's mosquitoes do what they do

Pittsburgh's three rivers, steep hollows and leafy neighborhoods give it a humid summer and plenty of shaded standing water, and the Allegheny County Health Department finds West Nile in mosquito samples across several neighborhoods most summers, treating each one it finds.

  • Three rivers and their hollows: shaded creek bottoms and river banks hold water and humidity.
  • Tree canopy: the Asian tiger mosquito breeds in gutters and containers in the city's leafy neighborhoods.
  • Catch basins: urban Culex pipiens breed in storm drains; the county treats where samples test positive.
  • Short season: June through September; the index is zero from October to May.

A typical year in Allegheny County

What the Bite Index typically reads here each month, from Allegheny County's 30-year climate normals run through the same model as today's number. The month you're in is marked; the season map shows the same long-run picture for every county.

  1. JJanuary: 0
  2. FFebruary: 0
  3. MMarch: 0
  4. AApril: 0
  5. MMay: 12
  6. JJune: 49
  7. JJuly: 65
  8. AAugust: 65
  9. SSeptember: 48
  10. OOctober: 8
  11. NNovember: 0
  12. DDecember: 0

Local surveillance and West Nile virus

The Bite Index measures nuisance biting, not disease. Allegheny County's health department traps and tests mosquitoes through the season and publishes positive West Nile pools by ZIP code. When your ZIP has an active advisory, follow it regardless of today's number.

How the Bite Index is scored

The index is a model of conditions, not a mosquito count. Warmth and water set the size of the population, tonight's weather sets how much of it flies, and the season and local reports adjust the result. Every factor and today's value for it is listed here so you can check the number yourself. Warmth and Water are exactly the climate core of our county-level mosquito season map; the map shows that core on 30-year normals for every county, and “typical for this month” is the same model run on this county's normals, so the comparison is like for like.

WWater

Rain over the egg-to-adult window (4.3 in. between Oct 8 and Oct 23), expressed as a monthly rate on the same wetness curve the season map uses. At summer temperatures eggs become biting adults in about a week, so today's mosquitoes are last week's rain. Cool weather stretches the window; hot dry days shrink it. Irrigation, creeks and pools keep a 35% floor even in a drought.

Role scales
Today 100%

TWarmth

The trailing two-week average temperature on the season map's curve: nothing below 50°F, full speed at 78–88°F, a small penalty in extreme heat. Multiplied with Water, so a cool fortnight caps the index however wet it has been.

Role gates
Today 24%

ATonight

Whether the population that exists will actually fly and bite this evening: dusk temperature (65–85°F is ideal), wind (they stop flying around 10 mph), humidity, and rain around sunset. Scales the index between half and full.

Role 0.5–1×
Today 0%

GGround truth

A nudge from local trap counts and reports when we have them. For Pittsburgh this is neutral today; the health department's surveillance is linked above and will feed this factor as we wire it in.

Role ±15%
Today neutral

SSeason gate

A multiplier from the calendar: fully open in the city's season months, half-open in the shoulder months, nearly closed in deep winter unless the week is warm. Below a 50°F weekly average the index is simply 0.

Role ×
Today 15%

index = 100 × S × [T × (0.35 + 0.65·W)] × (0.5 + 0.5·A) × (1 + 0.15·G)

Bands: Low 0–20 · Moderate 21–40 · High 41–60 · Very High 61–80 · Severe 81–100. Weather is from Open-Meteo (observations and the 7-day forecast), refreshed hourly. The lag and temperature thresholds follow published work on Culex and Aedes development (Rueda et al. 1990; Cornell NRCC degree-day emergence; JAMCA 2024 on rainfall two to four weeks before trap peaks).

Questions people ask about mosquitoes in Pittsburgh

When is mosquito season in Pittsburgh?
June through September, peaking in July and August. Frost, usually October, ends it.
Why do the hollows and parks feel worse?
Pittsburgh's ravines trap humidity and shade standing water, which is exactly what Culex and the Asian tiger mosquito want. Frick Park and the river trails run above the citywide index at dusk.
Is West Nile virus a risk in Pittsburgh?
Yes. Allegheny County finds positive samples in several neighborhoods most summers and treats them. Its announcements are authoritative; follow them over the index.
Where does this forecast's data come from?
Open-Meteo weather for downtown Pittsburgh, scored by our documented model with the northern breeding lag. Not a trap count.

Also covers Mount Lebanon, Bethel Park, Monroeville, Ross Township, Penn Hills, Sewickley, Frick Park, the North Shore: the forecast point is central Pittsburgh, and conditions within about 30 miles track it closely. Weather fetched Nov 8, 5:28 PM local time.

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